SNR, a better way to give a signal report

Or why I believe a 59 report is meaningless!

Receiving an S9 signal doesn't automatically mean that the signal is clear and intelligible. The S-meter (or signal strength meter) gives us a snapshot of the signal strength, but it doesn't tell us anything about the Noise Level (NL) or the Signal to Noise-Level Ratio (SNR), which are crucial in understanding the overall quality of the received signal. A signal might be strong in terms of the S-meter, but if the noise level is similarly high, then the actual communication may be difficult or unclear. Most of today's operators will add an Audio quality report of 5, to make the report 59 which in amateur jargon means that the received transmission supposed to be of excellent quality e.g., an excellent signal. However, to often we hear stations giving a report of 59 or even 59+ only to go on to request a retransmission. Audio quality reports have a scale from 1 to 5 and are given by the operator. With 5 being excellent and 1 being very poor. This relies heavily on the operators HSP, and as we all have experienced, those "Audio reports are ...." well let's say that those reports are not very reliable.

For instance, if the noise level at the receiving station is S8, and the received signal is S9, the SNR would only be 6 dB. Which would mean that the signal is just slightly stronger than the noise. This could make understanding the transmission challenging, even if it shows up as S9 on the meter. On the other hand, if the noise level is low (say S3) then an S9 signal would be much clearer as the SNR is now 6x better i.e. 36dB vs 6dB. 

The Importance of SNR

SNR (Signal to Noise-Level Ratio) gives us a much better sense of how usable a signal is as it compares the strength of the desired signal to the current background noise. A high SNR means that the signal is much stronger than the noise, making it easier to decode and work with. On the other hand, a low SNR means the noise is almost as strong or stronger than the signal, which can lead to poor communication quality or to a completely unreadable signal.

To calculate the SNR we need two signals, the noise level  and the signal strength of the received transmission, both numbers need to be a power level (dB). And since the levels will be rather small we'll use the Decibel in milli Watts e.g, in dBm.

Determining the Noise Level

Determining the Noise Level (NL) of our receiving system is rather easy, all we have to do is tune to a channel where no signal is present and record the S-Value, as shown in the below picture. 

Next we tune to a channel with a transmission and note the recived signal, say S9+10 as depicted below.

Converting S-Values to Power

From the IARU Technical Recommendation R.1:

S1 corresponds to -121 dBm

S9 corresponds to -73 dBm

 And the steps between S-Units are in 6 dB increments. This means:

S1 to S2 = -121 dBm to -115 dBm (6 dB increase)

Above S9 we tend to add a dB value to the S9 value, i.e. 

S9 to S9+10 = -73 dBm to -63 dBm (10 dB increase) 

 

click to view larger file

So, to calculate the SNR:

1. Convert both, the received signal strength and the noise level into power levels (dBm).
2. Calculate the difference between the received signal and the noise level (e.g., SNR = Signal Power - Noise Level).

Using the above values:

Using the above graph we convert the received noise level of S4 to a power level of -103dBm and the received signal level of S9+10 to -63dBm. 

Using the below formula:

 

SNRdB = (Signal-LeveldBm) - (Noise-LeveldBm) 

  

SNR = (-63) - (-103)

 

SNR = 40 dB

This would mean that the signal is 40 dB above the noise level, which is a strong signal and would be very clear.

Conversely, if the received signal would be S9 (-73 dBm) and the noise level would be S8 (-79 dBm), the SNR would only be 6 dB.

While still a reasonable SNR, it would be somewhat noisier than the 9+10 example, and we might find that we would need to ask for a repeat transmission occasionally.

Potential Benefits of Using SNR instead of S-Meter Values

• More Accurate Representation of Signal Quality: 

SNR considers both the signal strength and the noise level, which gives a much clearer idea of the actual quality of the communication link.

• Increased Context: 

By reporting SNR, operators would have more information about whether the signal is being received clearly or if noise is impacting communication.

• Noise Awareness: 

Instead of just reporting a S9 signal, one could be aware of how much noise is present at the receiving station. This could help with adjusting the transmitting stations output power, e.g. increasing the output from 100W to 400W, which is a power level increase of 6dB and as such should, in principal, add 6dB to the SNR.

 

Remember bigger SNR = better signal quality.

Challenges

• SNR requires additional measurements: 

To report SNR, operators would need to be able to measure or estimate the Noise Level  (NL) at their location. This can be challenging if the equipment doesn't provide this information directly. Most modern SDR systems do have the ability to read signal strength as a power or voltage level.

• S-meter and SNR are still subjective: 

While SNR is definitely more meaningful than just reporting an S-value, it still depends on the equipment's ability to measure signal strength and noise level accurately. Again, most SDR systems are very accurate.

Conclusion

Reporting 59 without any context of the noise level doesn't provide the full picture. Shifting to SNR as a primary metric would give operators a much better understanding of the quality of the received signal. It would not only account for the signal strength but also how well the signal stands out from the noise in the environment, leading to clearer communication and fewer misunderstandings.

Incorporating SNR reports into amateur radio communication could definitely improve clarity and signal quality perception. Perhaps this is something more operators could adopt in their day-to-day operations.

Most SDR (Software Defined Radio) already have the ability to report the signal strength as a power or voltage level. A few lines of code and the SNR could additionally be displayed.

Appendix

NOTE: The SNR changes with the receiver bandwidth however, for the purpose of a quality/signal report it is not nesseary to include the receiver bandwith. 

See https://vk5hw.blogspot.com/2022/02/lets-talk-about-receiving-signal-that.html

• HSP  = Human Signal Processor (normally found between the ears)

• IARU Technical Recommendation R.1
• Signal Level Strength Meter Calibration and IARU Standards
• Understand SINAD, ENOB, SNR, THD, THD + N, and SFDR so You Don't Get Lost in the Noise Floor 
• Signal strength and readability report
• Noise Counter-measures
• What is your S-Meter actually indicating
• S-Values are they useful
• A little history about S-Points
• How to achive receiver bliss

Do the old analog radios have better receivers than the new breed of SD-Radios?

I've had an interesting conversation this morning on 10m SSB. The conversation started about my audio being a bit "sharp" which, I guess, it might be at a 2.3kHz transmit bandwidth (200-2500) from my ICOM IC-7610. I've been explaining that I like to use less bandwidth to share our frequency spectrum more equally and avoid splattering across the spectrum. At which stage my QSO partner mentioned that he found me because I was splattering across the band whilst he was using his Kenwood TS-440. 

During the conversion he mentioned that he also had an IC-7610 and that he would like to get an audio report from me. So the TRX got switched and we progressed the QSO. To his amazement he found that I did not splatter on the ICOM. Yet he was adamant that the Kenwood would/should be the better receiver.

I was quite confused about this. Why would he think that? What would be the reason to buy one of the most modern radios, but believing that the old, and let's face it the TS-440 only have a good reputation amongst the CB fraternity, would outperform one of the more modern radios on this planet. 

Now, I have used quite a few Amateur radios in the past, the likes of an Elecraft K3 with added 2.8, 2.1 and 1.8kHz roofing filters, an ICOM IC-765 with Inrad roofing filter mod, Yaesu FT-5000MP with 2.7kHz roofing filter, even some of the newer, direct sampling SDRs like the ICOM IC-7300 and the ANAN 100D. Additionally I've owned and operated a DRAKE TR7, a Kenwood TS-520, a couple of YAESUs, the FT-101, FT-901/2, FT-757GX, FT-2000, FT-5000dx and an FT-817, also some ICOMs the likes of an IC-706, IC-730, IC-735, IC-7000, IC-7400. They all got purchased according to a few criteria but the main criteria was $$$ and then RX performance. These days a few more aspects have come to dictate the purchase of a new toy, but that is for another story.

Please note, that I'm not talking about LAB tests, even though I have done and still do receiver and transmitter test to get to know what the radio is capable of in my environment. I'm talking about the day to day use of these radios at an average QTH with average antenna systems. Most of these radios are far better than a Kenwood TS-440, which I might add I had the privilege of using during a contest and a field-days (what a debacle that was), only the FT-757GX I'd say was worst in the TX and RX department than the TS-440 and maybe the IC-706 in the TX department but this was bought purley as a mobile rig. 

Anyway, based on my experience, I have to say that my answer to the question would be a resounding "definitely not in this case".

73 

UPDATE 12/2023: The operator is now using his IC-7610 and it is the best thing since sliced bread. Oh and he change his callsign from VKx1234 to VKx123 and no, no Licence upgrade.